The Ukrainian president, Volodymyr Zelenskyy, will deliver a virtual address to the US Congress on Wednesday, the latest in a series of speeches to western leaders as he works to galvanize support for his besieged nation.
The remarks to both chambers of Congress come on day 21 of the battle for Ukraine’s survival under an intensifying assault from Russia.
Russian troops are advancing on the Ukrainian capital, Kyiv, in a war that has already killed hundreds of civilians in aerial and artillery bombardment, including at least 100 children.
More than 3 million people have fled Ukraine since the invasion, causing the fastest-growing refugee crisis in Europe since the second world war.
Zelenskyy's speech follows similar addresses to the UK parliament, in which he invoked Shakespeare and echoed Winston Churchill's famous wartime oration to the House of Commons about defiance in the face of an apparently overwhelming aggressor.
On Tuesday, Zelenskyy appealed to Canada's parliament, and the nation's large Ukrainian diaspora, to rally behind his country.
That evening, the prime ministers of NATO allies and Russian neighbours Poland, the Czech Republic and Slovenia travelled by train to Kyiv, which was under a 35-hour curfew as Russian shells and missiles rained down on the capital, striking residential areas and civilian infrastructure.
It came on the same day Zelenskyy acknowledged that Ukraine’s longstanding hope of joining Nato was unlikely.
"For years, we heard about the apparently open door, but have already also heard that we will not enter there, and these are truths and must be acknowledged," the Ukrainian president said in a speech before the leaders of the Joint Expeditionary Force, a UK-led initiative bringing together 10 north Atlantic countries to create a capability for responding rapidly to crises.
In his remarks on Wednesday, which will come nearly two weeks after Zelenskyy met virtually, behind the scenes, with a small group of members of Congress, he is expected to call on the US once again to "close the skies" over Ukraine.
He is also likely to press to be supplied with fighter jets by NATO allies that Ukrainian pilots can fly up against Russian air forces, and steeper economic sanctions in the face of an advancing Russian assault.
The Biden administration has so far flatly ruled out an option of the west imposing a no-fly zone over the country, determined to avoid inevitable direct combat between the US and Russian forces – a conflict the US president has said would lead to "World War Three".